Chalcogen alloying mediated electronic structure modulation in ultrathin Nb(S x Se (1− x ) ) 2 nanosheets for the hydrogen evolution reaction

Modulating the electronic structure of transition metal dichalcogenides (TMDs) especially by regulating the d-electrons implicitly escalates their catalytic properties. In this respect, chalcogen alloying has proven to be a prime strategy in engineering the d-band electronic structure of transition metals in TMDs. Herein, we report composition tuning of Nb(S x Se (1− x ) ) 2 alloy nanosheets (NSs) via colloidal synthesis and demonstrate the role of modulating d-electron density and defect engineering in alloy structures for the hydrogen evolution reaction (HER). Introducing sulphur (S) in the NbSe 2 lattice optimizes its electronic properties for enhanced HER activity. Both experimental and density functional theory (DFT) calculations uncover the modulation in the d-band electronic structure and emphasize chalcogen vacancies as active sites for facile adsorption–desorption in the HER process. Additionally, substitutional alloying of the smaller size S atom in NbSe 2 induced lattice contraction leads to a local polarized electric field in the basal plane. Cumulatively, with modulation of the electronic structure and lowering of the energy barrier, the x = 0.5 (NbSSe) composition exhibits higher HER activity than both NbSe 2 and NbS 2 NSs. The increase in catalytic activity with chalcogen alloying is also verified by the Gibbs free energy of hydrogen adsorption (Δ G H * ) being close to thermoneutral for the alloyed catalyst.